1. Field of the Invention
The present invention relates to a recording ink set which is used for an ink-jet printer and includes a combination of different color inks.
2. Description of the Related Art
The ink discharge system, which has been hitherto known for the ink-jet recording system, includes, for example, the electrostatic attraction system, the system in which mechanical vibration or displacement is applied to the ink by using a piezoelectric element or the like, and the method in which bubbles are generated by heating the ink to utilize the pressure generated thereby. Ink droplets are formed by means of the discharge system as described above, and all or a part of the droplets are adhered to a recording objective such as paper to perform the recording. Those known and used as the ink to be employed for the ink-jet recording system as described above include those in which a variety of water-soluble dyes or pigments are dissolved or dispersed in liquid media each comprising water or a combination of water and water-soluble organic solvent.
In order to adequately perform the recording for a long period of time by using the ink as described above, for example, the following conditions are required. That is, the characteristic values including, for example, the viscosity, the surface tension, the electric conductivity, and the density of the ink to be used are appropriate values. In order to avoid any clog-up at the nozzle or the orifice of the recording apparatus, no deposited matter is generated and no physical property value is changed by the influence of heat or the like. Further, the recorded image is excellent, for example, in water resistance and light resistance. A large number of suggestions have been made in order to satisfy the conditions as described above.
However, in recent years, it is more demanded to perform the recording on the regular paper rather than on the exclusive ink-jet paper in view of the cost and the consideration of the environment. In the case of most of the conventional inks, when the recording is performed on the regular paper, the color bleed is apt to occur, which is caused such that the inks of different colors are mixed with each other at portions at which the different colors are adjacent to one another. As a result, a problem arises in that the printing quality is deteriorated.
The present invention has been made in order to solve the problem as described above, an object of which is to provide a set comprising recording inks with which the color bleed is reduced even when the recording is performed on the regular paper.
According to a first aspect of the present invention, there is provided an ink set for ink-jet recording having a combination of inks of different colors, comprising:
a first ink which contains water, a first coloring agent, and a water-soluble organic solvent; and
a second ink which contains water, a second coloring agent different from the first coloring agent, and a water-soluble organic solvent, wherein:
a solubility parameter xcex41 of the water-soluble organic solvent contained in the first ink satisfies a relationship of 4xe2x89xa6|xcex41xe2x88x92xcex42| with respect to a solubility parameter xcex42 of the water-soluble organic solvent contained in the second ink.
In general, the bleeding, which is caused at the boundary between inks such as black and yellow, is relatively conspicuous. In the ink set of the present invention, in order to avoid the bleeding as described above, it is desirable that the first ink is a black ink containing a black coloring agent, and the second ink is a color ink, for example, a cyan, magenta, or yellow ink containing a color coloring agent other than the black coloring agent. The ink set may further comprise third and fourth coloring agents having colors different from those of the first and second coloring agents respectively. It is necessary that the water-soluble organic solvents contained in the first ink and the second ink of the ink set of the present invention have their solubility parameters xcex41, xcex42 which satisfy the relationship of 4xe2x89xa6|xcex41xe2x88x92xcex42|. The water-soluble organic solvent in each of the inks may be based on a single species or a mixed system containing a plurality of species. However, even when a plurality of water-soluble organic solvents are contained in the first ink, it is necessary that any one of the water-soluble organic solvents contained in the first ink satisfies the relationship of 4xe2x89xa6|xcex41xe2x88x92xcex42 |for the solubility parameters xcex41, xcex42 with respect to the water-soluble organic solvent contained in the second ink. When a plurality of water-soluble organic solvents are contained in each of the first ink and the second ink, it is necessary that any one of the water-soluble organic solvents contained in the first ink satisfies the relationship of 4xe2x89xa6|xcex41xe2x88x92xcex42|for the solubility parameters xcex41, xcex42 with respect to any one of the water-soluble organic solvents contained in the second ink.
According to a second aspect of the present invention, there is provided an ink cartridge to be used for an ink-jet or ink-jetting type recording apparatus, comprising:
a first compartment which accommodates a first ink containing water, a first coloring agent, and a water-soluble organic solvent; and
a second compartment which accommodates a second ink containing water, a second coloring agent different from the first coloring agent, and a water-soluble organic solvent, wherein:
a solubility parameter xcex41 of the water-soluble organic solvent contained in the first ink satisfies a relationship of 4xe2x89xa6|xcex41xe2x88x92xcex42|with respect to a solubility parameter xcex42 of the water-soluble organic solvent contained in the second ink.
The water to be used in the present invention is not specifically limited. However, it is preferable to use water having high purity such as ion exchange water and distilled water excluding, for example, tap water. The content of the water may be determined depending on the type and the composition of the coloring agent and the water-soluble organic solvent or the characteristics of the desired ink. However, in general, it is preferable that the content is 10 to 97% by weight with respect to the total weight of the ink. If the content is less than 10% by weight, then the viscosity of the ink is too high, and it is difficult to discharge the ink from the head. If the content exceeds 97% by weight, the ink is apt to be dried. The content is more preferably 30 to 95% by weight, and much more preferably 40 to 90% by weight.
Those usable as the coloring agent to be used in the present invention include, for example, dyes and pigments. Those usable as the dye include, for example, water-soluble dyes represented by direct dye, acidic dye, basic dye, and reactive dye. The water-soluble dye is not specifically limited. However, it is preferable to use those which are adequate for the ink to be used for the ink-jet recording system and which satisfy required performance such as vividness, water solubility, stability, light resistance, and other required performance, including, for example, C. I. Direct Black 17, 19, 32, 51, 71, 108, 146, 154, 168; C. I. Direct Blue 6, 22, 25, 71, 86, 90, 106, 199; C. I. Direct Red 1, 4, 17, 28, 83, 227; C. I. Direct Yellow 12, 24, 26, 86, 98, 132, 142; C. I. Direct Orange 34, 39, 44, 46, 60; C. I. Direct Violet 47, 48; C. I. Direct Brown 109; C. I. Direct Green 59; C. I. Acid Black 2, 7, 24, 26, 31, 52, 63, 112, 118; C. I. Acid Blue 9, 22, 40, 59, 93, 102, 104, 113, 117, 120, 167, 229, 234; C. I. Acid Red 1, 6, 32, 37, 51, 52, 80, 85, 87, 92, 94, 115, 181, 256, 289, 315, 317; C. I. Acid Yellow 11, 17, 23, 25, 29, 42, 61, 71; C. I. Acid Orange 7, 19; C. I. Acid Violet 49; C. I. Basic Black 2; C. I. Basic Blue 1, 3, 5, 7, 9, 24, 25, 26, 28, 29; C. I. Basic Red 1, 2, 9, 12, 13, 14, 37; C. I. Basic Violet 7, 14, 27; and C. I. Food Black 1, 2.
The pigment is not specifically limited provided that the pigment is capable of being dispersed in the aqueous phase. The pigment includes, for example, azo pigment such as azo lake, insoluble azo pigment, condensed azo pigment, and chelate azo pigment; polycyclic pigment such as phthalocyanine pigment, perylene, perynone pigment, anthraquinone pigment, quinacridone pigment, dioxazine pigment, thioindigo pigment, isoindolinone pigment, and quinophthalone pigment; dye lake such as basic dye type lake and acidic dye type lake; organic pigment such as nitro pigment, nitroso pigment, and aniline black daylight fluorescent pigment; and inorganic pigment such as titanium oxide, iron oxide-based pigment, and carbon black-based pigment. For example, those obtained by applying a surface treatment to the various pigments described above, for example, with a surfactant or a macromolecular dispersing agent can be also used as the pigment to be used in the present invention. Such a material includes, for example, graft carbon.
When the pigment as described above is used as the coloring agent to be used in the present invention, a dispersing treatment is performed in accordance with a conventionally known method together with an appropriate dispersing agent, a solvent, pure water, and optionally other additives. Those usable as the dispersing agent include, for example, a surfactant and a macromolecular dispersing agent to be used to disperse the pigment as described in Japanese Patent Application Laid-Open No. 62-101672. The macromolecular dispersing agent is not specifically limited, including, for example, protein such as gelatin and albumin; natural rubber such as gum arabic and gum traganth; glucoside such as saponin; cellulose derivative such as methyl cellulose, carboxy cellulose, and hydroxymethyl cellulose; natural macromolecule such as lignosulfonate and shellac; anionic macromolecule such as salt of polyacrylic acid, salt of styrene-acrylic acid copolymer, salt of vinylnaphthalene-acrylic acid copolymer, salt of styrene-maleic acid copolymer, salt of vinylnaphthalene-maleic acid copolymer, and sodium salt and phosphoric acid salt of xcex2-naphthalenesulfonic acid-formalin condensate; and nonionic macromolecule such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyethylene glycol.
The surfactant includes, for example, anionic surfactant such as higher alcohol sulfuric acid ester salt, liquid fatty oil sulfuric acid ester salt, and alkylarylsulfonic acid salt; and nonionic surfactant such as polyoxyethylene alky ether, polyoxyethylene alkyl ester, sorbitan alkyl ester, and polyoxyethylene sorbitan alkyl ester. The dispersing agent may be used singly, or two or more of the dispersing agents may be used in combination. It is preferable that the dispersing agent is generally blended in an amount of 0.01 to 20% by weight with respect to the total weight of the ink. If the blending amount is less than 0.01% by weight, an effect such as adjustment of surface tension or the like is not sufficiently expressed. If the blending amount exceeds 20% by weight, then the effect is not only enhanced, but also any harmful influence such as increase in ink viscosity appears in some cases.
The dispersing machine, which is used for the dispersing treatment for the pigment as described above, is not specifically limited. It is possible to widely use general dispersing machines. However, the dispersing machine includes, for example, ball mills, roll mills, and sand mills. Especially, it is preferable to use a high speed type sand mill. The dye and the pigment may be used singly respectively. Alternatively, two or more dyes, two or more pigments, or two or more dyes and pigments may be mixed and used. It is preferable that the content of the coloring agent is generally 0.1 to 20% by weight with respect to the total weight of the ink. If the content is less than 0.1% by weight, it is difficult to sufficiently develop the color on the regular paper. If the content exceeds 20% by weight, the coloring agent is deposited and/or aggregated in the ink in some cases. The content is more preferably 0.3 to 1.5% by weight, and much more preferably 0.5 to 10% by weight.
The water-soluble organic solvent to be used in the present invention is not specifically limited, including, for example, alkyl alcohol having a number of carbon or carbons of 1 to 5 such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and n-butyl alcohol; amide such as dimethylformamide and dimethylacetoamide; ketone or ketone alcohol such as acetone and diacetone alcohol; ether such as tetrahydrofuran and dioxane; alkylene glycol containing alkylene group having a number of carbons of 2 to 6 such as ethylene glycol, propylene glycol, triethylene glycol, and diethylene glycol; glycerol; polyalkylene glycol such as polyethylene glycol and polypropylene glycol; lower monoalkyl ether of polyhydric alcohol such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, and triethylene glycol monomethyl (or ethyl) ether; lower dialkyl ether of polyhydric alcohol such as triethylene glycol dimethyl (or ethyl) ether; sulfolane, pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and 1,5-pentanediol. The water-soluble organic solvent as described above may be used singly. Alternatively, two or more of the water-soluble organic solvents as described above may be used in combination. When two or more species of the water-soluble organic solvents are used in combination in one ink (first ink), it is necessary that each of the water-soluble organic solvents satisfies the relationship of solubility parameter as described later on with respect to the water-soluble organic solvent contained in the other ink (second ink).
The content of the water-soluble organic solvent is not specifically limited provided that the water-soluble organic solvent is contained abundantly in an amount next to the amount of water. The content of the water-soluble organic solvent may be determined within a wide range depending on the composition of the ink or the desired characteristics of the ink. However, it is preferable that the water-soluble organic solvent is contained in an amount of not less than 3% by weight. If the content of the water-soluble organic solvent is less than 3% by weight, the color bleed-suppressing effect is not sufficiently expressed when the ink makes contact with another adjacent ink. The content is more preferably 3 to 40% by weight, and much more preferably 5 to 30% by weight.
The water-soluble organic solvents, which are contained in the black ink and the color ink included in the ink-jet recording ink set of the present invention, are used in combination so that the water-soluble organic solvents are different from each other in solubility parameter by not less than 4. In this specification, the solubility parameter (xcex4) refers to the value calculated by the following calculation expression of Fedors from the molar volume (xcex94vi) and the evaporation energy (xcex94ei) of the atom or the atomic group of the chemical structure.
[xcex4=(xcexa3xcex94ei/xcexa3xcex94vi)xc2xd]xe2x80x83xe2x80x83(Expression of Fedors) 
Besides the solubility parameter being determined by the calculation from the chemical composition as described above, the solubility parameter can be also determined from actually measured values including, for example, the calculation from the evaporation heat, the calculation from the refractive index, the calculation from the kauri-butanol value, and the calculation from the surface tension.
Usually, the water-soluble organic solvents are readily compatible when the values of the solubility parameters are close to one another. The water-soluble organic solvents are hardly compatible when the difference in value is large. If the difference in numerical value is less than 4, no sufficient suppressing effect is expressed on the color bleed. The effect is observed when the difference in value is not less than 4. Usually, those having a difference of 4 to 10 are preferably selected. When two or more of the color inks are contained in the ink set for the ink-jet recording of the present invention, the solubility parameters of the water-soluble organic solvents contained in the respective color inks may be identical.
Preferred combinations of the water-soluble organic solvents include, for example, a combination of ethylene glycol (xcex4=17.8) and 1,3-butanediol (xcex4=11.6), a combination of ethylene glycol (xcex4=17.8) and 2-pyrrolidone (xcex4=13.1), a combination of glycerol (xcex4=20.2) and 2-pyrrolidone (xcex4=13.1), a combination of glycerol (xcex4=20.2) and diethylene glycol (xcex4=15.0), a combination of diethylene glycol (xcex4=15.0) and diethylene glycol monoethyl ether (xcex4=10.9), and a combination of polypropylene glycol (xcex4=10.3) and diethylene glycol (xcex4=15.0).
Additionally, the ink contained in the ink set for the ink-jet recording of the present invention may optionally contain, for example, hitherto known various types of dispersing agents, surfactants, viscosity-adjusting agents, surface tension-adjusting agents, pH-adjusting agents, antiseptic agents, and fungicides. When the ink set for the ink-jet recording of the present invention is used for the ink-jet recording method of the type in which the recording liquid is electrically charged, it is also preferable to contain specific resistance-adjusting agents including, for example, inorganic salts such as lithium chloride, ammonium chloride, and sodium chloride. Further, when the ink set for the ink-jet recording of the present invention is used for the ink-jet system of the type in which the ink is discharged in accordance with the action of the thermal energy, for example, it is also preferable to adjust values of thermal physical properties including, for example, the specific heat, the coefficient of thermal expansion, and the coefficient of thermal conductivity.
The problems involved in the conventional technique are sufficiently solved in the ink set for the ink-jet recording of the present invention obtained as described above. The color bleed is reduced in the ink-jet system. It is possible to provide the vivid color recording even on the regular paper.